The present invention relates to vehicle wheel alignment, and more particularly to vehicle wheel alignment systems which measure the locations and orientations of the vehicle wheels in a three dimensional coordinate system.
Various systems have been designed to determine vehicle wheel alignment angles. For example, U.S. Pat. No. Re 33,144 to Hunter and January and U.S. Pat. No. 4,319,838 to Grossman and January each describe a wheel alignment system which uses electro-optical transducers to determine the toe alignment angles of a vehicle. FIG. 2 of each of these patents shows six angle transducers carried by support assemblies which are mounted to the vehicle wheels. FIG. 4 of Re 33,144 and FIG. 9 of U.S. Pat. No. 4,319,838 show the geometry of this arrangement and illustrate the six angles which are directly measured. These patents further describe (see Re 33,144 col. 7 lines 26-39, and 4,319,838 col. 8 line 63 to col. 9 line 12) how the toe alignment angles are computed from the angles directly measured by the angle transducers.
U.S. Pat. No. 4,879,670 to Colarelli describes a gravity-referenced inclinometer. FIG. 3 of 4,879,670 illustrates the mounting of such an inclinometer to a vehicle wheel for measuring the camber of the wheel. The use of gravity-referenced inclinometers to measure camber is conventional, and assumes the vehicle rests while being measured on a surface which is both flat and level.
SAE Publication 850219, titled "Steering Geometry and Caster Measurement", by January, derives and discusses the procedures and methods by which toe and camber alignment transducers are used to determine the caster and steering axis inclination (SAI) of a vehicle. The procedures described therein are the industry standard.
Equipment of this general type and using the apparatus and methods enumerated above has been used world-wide for many years. Such equipment is capable of determining the camber, caster, and pointing or "toe" alignment angles of the wheels relative to one or more appropriate reference axes, and is sufficient to allow proper adjustment of the alignment so as to reduce tire wear and provide for safe handling. It is believed, however, that such equipment could be improved.
U.S. Pat. No. 5,488,472 to January advances the art further by describing the use of conventional toe transducers which, while operating in cooperative pairs, have the additional capability of measuring the distances, each relative to the other. FIG. 7 of U.S. Pat. No. 5,488,472 illustrates the use of these "range and bearing" measurements to determine the coordinates and orientations of the sensors and wheels in a two dimensional coordinate system.
FIGS. 8 through 11 of U.S. Pat. No. 5,488,472 illustrate the seriousness of the central problem in measuring the individual toe alignments of vehicle wheels, namely that individual toe of a vehicle wheel is defined to be relative to a longitudinal reference axis, but the definition of that reference axis may not be arbitrarily chosen by the designer of such equipment. In general, two such reference axes are used, the definitions of which were standardized long ago in the automotive service industry.
The individual rear toe alignment angles are defined to be relative to a reference axis commonly known as the "geometric centerline". This line, illustrated and labeled "CL" in FIG. 9B of U.S. Pat. No. 5,488,472, is practically determined as the bisector of the angle formed by the longitudinal lines of sight of the toe transducers. These lines of sight are illustrated and labeled 48 and 50 in FIG. 6 of U.S. Pat. No. 5,488,472. A key aspect of this definition is that the forward endpoints of these longitudinal lines of sight are remarkably insensitive to small changes in the steering directions of the front wheels, which means that the individual rear toe alignment measurements are similarly insensitive to the steering of the front wheels.
The layman's definition of the geometric centerline is the line joining two points, one lying halfway between the front wheels and the other lying halfway between the rear wheels. This line very closely approximates the centerline described above and is very easy to visualize.
The individual front toe alignment angles are defined to be relative to a reference axis commonly known as the "thrust line". This line, illustrated and labeled "TL" in FIG. 9A of U.S. Pat. No. 5,488,472, is practically determined as the bisector of the angle formed by the reference axes of the rear longitudinal toe transducers. These reference axes are illustrated and labeled 59 and 60 in FIG. 9A of U.S. Pat. No. 5,488,472. A key aspect of this definition is that the thrust line is determined as the net pointing direction of the rear wheels, which means that the individual front toe alignment measurements are intentionally sensitive to the toe alignment of the rear wheels.
The layman's definition of the thrust line is the line which bisects the angle formed by the planes of rotation of the rear wheels. This line is very easy to visualize.
There are great practical advantages in determining toe alignment relative to these reference axes. Firstly, the toe adjustment of the rear wheels can be accomplished with the front wheels steered only approximately straight ahead. Secondly, the thrust line thus determined is approximately the line down which the center of the rear axle travels when the vehicle moves in a straight line, and this line is made to point approximately down the centers of the front and rear axles. Thirdly, the toe adjustment of the front wheels can be accomplished with the steering wheel held straight such that the front toe measurements are symmetric about the thrust line, thereby insuring that the steering wheel is straight when the vehicle moves in a straight line. Fourthly, vehicle manufacturers have long provided toe alignment specifications which are relative to these reference axes. Any vehicle alignment system which defines toe alignment relative to other axes will not be able to correctly align the vehicle as specified by the vehicle manufacturers.
The disclosure of U.S. Pat. No. 5,488,472 illustrates that determining the two dimensional coordinates of the vehicle wheels does not provide greater ability to determine the toe alignments of the wheels relative to the appropriate reference axes of the vehicle. The only determinations of these reference axes which are practical to use are the same as those provided by transducers which measure angles but do not additionally measure distances.
U.S. Pat. Nos. 4,745,469 and 4,899,218, both to Waldecker et al., describe what is commonly known as an "external reference aligner". U.S. Pat. No. 4,899,218 is a continuation of U.S. Pat. No. 4,745,469, and contains no new disclosure. FIGS. 3 through 6 of these patents show how lasers are used to illuminate the tires and video cameras are used to examine images of the sidewalls. These patents further describe how "machine vision techniques" are used to examine the images and determine the distances between the cameras and certain locations on the sidewalls, thereby allowing a determination of the locations and orientations of the wheels in a coordinate system which is relative to the cameras.
Unfortunately, both U.S. Pat. Nos. 4,745,469 and 4,899,218 are woefully deficient in describing how a determination is made of the toe alignment of the wheels relative to the appropriate reference axes of the vehicle. The need for this is discussed in U.S. Pat No. 4,745,469, col. 2, lines 19-24:
"This wheel position information can be combined with similarly measured data defining the vehicle center line or other desired references and the complete vehicle alignment geometry can be analyzed and dynamically displayed on a meter or the like to guide an operator in adjusting or setting the wheel alignment." PA1 "The spatial position of the wheel . . . may be defined in relation to . . . a longitudinal line L which passes through two fixed points on the vehicle. For convenience, longitudinal line L is shown extending through the front and rear bolts 24 and 26 which attach the control arm to the vehicle chassis. . . . In FIG. 1, a second longitudinal line L' is drawn parallel to longitudinal line L so that it passes through wheel axis A. The angle between longitudinal line L' and the center plane C establishes the toe-in of the wheel." PA1 "Once two points in real space have been found, corresponding to two points along a horizontal line on the tire, the toe-in is easily computed using trigonometry. Referring to FIG. 21, the left and right sensor modules 36 are illustrated together with a portion of the tire 12. Each sensor is a predetermined distance from a reference point REF. The distances are designed Y.sub.L and Y.sub.R. The spacing between the left and right data points P.sub.L and P.sub.R is therefore Y.sub.L +Y.sub.R. The real space position of points P.sub.L and P.sub.R in the Z direction are the measured values Z.sub.L and Z.sub.R determined by the conversion from image space data to real space data. If the points P.sub.L and P.sub.R do not have the same Z coordinates, then there is a non-zero toe angle. This angle is determined by trigonometry as the arc tangent of the difference (Z.sub.R -Z.sub.L) divided by the sum (Y.sub.R +Y.sub.L)." PA1 "These parameters are given essentially by the spatial position of the wheel suspension (steering axle) relative to the wheel plane or to vertical or horizontal reference planes." and PA1 ". . . the spatial positions of the wheel plane and of the steering axle and, from the appropriate data as well as the stored positional data of the video camera tube and the wheel dimensions, the wheel axle and steering geometry data are determined electronically on the basis of consecutively obtained measurement results, taking into consideration known mathematical relationships." and PA1 "Because of the conical section geometry as well as the circle-ellipse affinity, the axis of the body of rotation and, with that, the spatial axis of the wheel suspension, that is, the steering axis as well as the spatial position of the wheel plane, can be determined from the different positions of the wheel and the data of the wheel axles and the steering geometry calculated from the mutual allocation or the allocation to the vertical or horizontal reference planes." PA1 "As has been described above, once the location of the target planes on the wheels is known, by rotating the wheels, the axis of rotation of the wheels can be determined, and from there, the alignment of the wheels." PA1 "So, for example, the apparatus could define a reference point for each wheel with the referent point being located at, say, the intersection of the axis of rotation of the wheel, with that wheel. These points can then be processed to define an approximately horizontal reference plane, relative to which the alignment of the wheels can be calculated."
Beyond this, U.S. Pat. No. 4,745,469 has no disclosure of how the toe measurements are determined relative to the vehicle center line. A reference line L is defined in FIG. 2 and discussed in col. 4, lines 13-23:
This is not believed to be a useful definition for a reference axis for determining toe alignment. Firstly, not all vehicles have an upper control arm with mounting bolts as described. Secondly, vehicles which have such upper control arms have one for the left front wheel and one for the right front wheel, and thus would have two different such lines L, even though left front toe and right front toe should be determined relative to the same reference axis. Thirdly, vehicles which mount an upper control arm in the manner illustrated in FIG. 2 of U.S. Pat. No. 4,745,469 commonly use shims, eccentric cams, or elongated slots to move these mounting bolts, thereby adjusting camber and/or caster of the affected wheel. Fourthly, no vehicle manufacturer specifies toe alignment relative to such an axis.
U.S. Pat. No. 4,745,469 describes determining the toe alignment of a wheel in yet another way in col. 16, lines 10-25:
This definition would have individual toe measured relative to the video cameras, which would provide the proper value only if the vehicle were squarely aligned relative to the cameras, which is highly impractical.
It is readily apparent from U.S. Pat. Nos. 4,745,469 and 4,899,218, in light of U.S. Pat. No. 5,488,472, that it is not sufficient merely to determine the locations and orientations of the vehicle wheels in a three dimensional coordinate system. Proper attention must be paid to determining the toe alignment of the wheels relative to the appropriate reference axes.
German Patent DE 29 48 573 A1, assigned to Siemens AG, describes the use of video cameras to determine the locations and orientations of the wheels of a vehicle. On each side of the vehicle, a single camera is moved to multiple positions to view the vehicle wheels. Alternatively, a single fixed camera is used at each side in conjunction with movable mirrors, or multiple cameras are used. The system examines the images thus viewed of the wheels of the vehicle to determine the locations and orientations of the wheels, from which the wheel alignment parameters are determined.
This patent provides scant details concerning how the wheel alignment parameters are determined from measurements made by the video cameras. For example
This disclosure also fails to describe how individual toe alignment measurements are determined from the wheel position data. Note that this patent application was filed Dec. 3, 1979, a time when four wheel vehicle alignment embodying thrust line alignment of the rear wheels was in its relative infancy.
European Patent Application PCT/US93/08333, filed in the name of Jackson and published under the Patent Cooperation Treaty as WO 94/05969 (hereinafter referred to as WO document 94/05969), describes the use of a video camera having one or more defined fields of view to view optical targets of known configurations which are mounted to the vehicle wheels. Through the use of sophisticated image recognition methods, the three dimensional coordinates and orientations of the vehicle wheels and their corresponding axes of rotation are determined. The wheel alignment parameters are determined from these coordinates and orientations.
This application treats the determination of individual toe alignment and individual camber alignment sketchily. See, for example, page 7, lines 28-34:
". . . the processor relates the dimensions of certain known geometric elements of the target with the dimensions of corresponding elements in the perspective image and by performing certain trigonometric calculations (or by any other suitable mathematical or numerical methods), calculates the alignment of the wheels of the vehicle."
See also page 25, lines 1-4:
A hint as to how this is performed is found on page 40, lines 2-8:
Although there is considerable disclosure in the WO document 94/05969 concerning how to determine the coordinates and orientations of the wheels and their axes of rotation in a three dimensional coordinate system, there is no disclosure which explains how the toe alignment or camber alignment is determined from those coordinates and orientations. As has been made clear above, this is not a trivial subject.
There is further a fundamental flaw in this methodology. Quite simply, the three-dimensional coordinates of the vehicle wheels, and the axes about which they rotate, are not sufficient to properly determine the wheel alignment parameters of the vehicle unless the plane representing the surface on which the wheels roll is also known in that coordinate system. Firstly, the camber, caster, SAI, and toe alignment parameters of the wheels are defined relative to this plane. Secondly, the WO document 94/05969 does not provide any method or apparatus for determining where this plane is in its coordinate system, even in the most general terms. The subject is not discussed therein. As will be made more apparent presently, handling, tire wear, stability, and safety issues are compromised thereby.
There exists a clear need for apparatus and methods which allow a proper determination of the alignment of the vehicle wheels, per their conventional and accepted definitions, using measurements of the three dimensional coordinates of the vehicle wheels, the axes about which they rotate, and the plane on which they roll.
In addition to the above-mentioned drawbacks, proper alignment using video systems is critically dependent upon accurate determination of the positions of the targets in the field of view. In those instances where all the targets move vertically in a uniform amount, that movement may be misinterpreted as one or more changes in alignment angles. Algebraically compensating for such motion in the field of view is not a trivial problem.